CAIRO — A court in Bahrain upheld the conviction of a prominent human rights activist on Tuesday, sentencing him to two years in a case that has exposed the government to international criticism and was seen as a crucial test of the monarchy’s repeated pledges to allow greater political freedom.

The activist, Nabeel Rajab, had been sentenced in August to three years in prison on charges of inciting antigovernment protests. On Tuesday, a judge dismissed one of the charges against Rajab, who has been incarcerated since August, reducing the sentence to two years from three, according to Rajab’s brother.